The present invention relates to a gas operated device for activating the reloading mechanism of an automatic rifle. More particularly, to such a device comprising a cylinder fixed to the rifle barrel and having a closed end and an open end, a piston slidable in the cylinder, and a chamber formed within the cylinder between the piston and the closed end, the chamber communicating with the interior of the rifle barrel through a gas duct.
In known gas-operated devices of the above type, firing gases generated by the explosion of a cartridge in the rifle breech are bled off from the rifle barrel, through the gas duct, into the chamber between the piston and the closed end of the cylinder. The pressure of these gases operates the piston which in turn activates the reloading mechanism. The pressure of the gases which operate the piston depends on the explosive power of the cartridge, since the cartridges available commercially for use in sporting rifles vary widely in their quantity of power, the pressures on the piston also vary widely. Therefore, in order for such gas-operated devices to operate under the varying conditions, and particularly with low pressures of the order of 90-100 atmosphere, the reloading mechanism is usually especially designed to operate at such low pressures and maximum use is made of the energy of the gases by providing precision-made mechanical seals between the cylinder and piston.
This method of achieving a seal between the cylinder and piston has a number of disadvantages. Firstly, the making and assembly of such mechanical seals having the required degree of precision is extremely difficult and laborious. Secondly, due to the precision and tightness of the seal, when a cartridge giving high pressure firing gases (180 - 200 atmospheres) is used, the mechanical stresses exerted on the reloading mechanism of the rifle are so high that they can result in breakage, deformation or jamming of the mechanism. If the mechanism is not broken, the high pressure firing gases would at least reduce the working life of the mechanism considerably.
In order to overcome the above disadvantages, compensating and/or regulating devices, which absorb the excess kinetic energy of the piston, or selectively operable mechanical compensators which compensate for the different thrusts upon the piston, or pressure relief valves which discharge the excess pressure of the diverted gases, may be incorporated in such gas-operated rifles. The use of any of these compensating and/or regulating devices, complicates the functioning of the rifle and may make the mechanism even more prone to jamming, however, these devices do not ensure the desired safe functioning of the rifle however accurate the assembly and adjustment of the devices.
Therefore, an object of the present invention is to provide a gas-operated device for activating the reloading mechanism of an automatic rifle which may be used with a wide range of commercially available cartridges but which does not incorporate mechanical seals in the cylinder-piston coupling, nor involve the use of mechanical compensating or regulating devices.
According to the present invention there is provided a gas-operated device for activating the reloading mechanism of an automatic rifle, comprising a cylinder fixed to the rifle barrel, and having an open end and a closed end, a piston slidable in the cylinder, and a chamber formed within the cylinder between the piston and the closed end, the chamber communicating with the interior of the rifle barrel through a first gas duct, characterised in that there is provided an interstice coaxial with and between the piston and the cylinder, the interstice communicating with the said chamber and opening through at least one second gas duct into the interior of the rifle barrel at a position closer to the breech end of the barrel than the opening of the first gas duct into the rifle barrel.
Preferably, the piston has an annular groove in its surface such that in the fully inserted position of the piston in the cylinder, the or vents vent of the second gas duct into the interstice is opposite the groove.
When a cartridge is fired from a rifle equipped with a device according to the present invention portions of the firing gas are bled successively into the interstice between the cylinder and the piston and into the chamber between the piston and the closed end of the cylinder. Within the interstice and the chamber the gases expand, thereby lowering the pressure, to values dependent upon the respective volumes of the interstice and the chamber. The gases beld into the chamber attempt to escape through the interstice, but escape is prevented by the counterpressure of the gases bled previously into the interstice. Thus a `gaseous diaphragm` is created in the interstice which acts as a seal against the release of the gases from the chamber and results in almost total exploitation of the energy of these gases for moving the piston and operating the reloading mechanism of the rifle.
The position of the gaseous diaphragm in the interstice varies according to the value of the firing-gas pressure at the openings to the gas ducts in the rifle barrel, the relative dimensions of the gas ducts, the volume of the interstice between piston and cylinder, the volume of the chamber formed between the piston and the closed end of the said cylinder, and according to the ratio of these volumes. In practice, the dimensions of the ducts, interstice and chamber being predetermined, therefore, the position of the `gaseous diaphragm` in the interstice depends exclusively upon the pressure of the firing gases. When this pressure is low (90-100 atmospheres), the `gaseous diaphragm` is formed very close to the chamber but as the pressure of the firing gases increase the position of the said diaphragm moves towards the open end of the cylinder. When the pressure of the firing gases is very high (180-200 atmospheres) the counterpressure of the gases diverted directly into the interstice, while still impeding the escape of the gases diverted into the chamber, is no longer able to act as a gaseous sealing diaphragm. The gases can therefore escape, to a limited degree, through the interstice, so that the pressure on the piston is reduced, with consequent reduction of the force exerted by the piston on the reloading mechanism of the rifle.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.